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Best way to fix or reduce a 7" to a 6" hole in main vent for humidifier install?

I swapped out my Honeywell that the plastic just fell apart with one of the same. Had a hard time finding one online, but ebay came to the rescue. Well they had made a few changes, and the 6" flex line they sent is to small for the 7" hole already there. I looked at a reducer and there is not much room now for collars and adapters. I'm thinking about getting a 10" Sq piece of tin with a 6" hole in it, and RTV and screw that in place. Or do you know of something better to try?


  • bob_46bob_46 Member Posts: 813
    Your solution sounds fine.
  • lchmblchmb Member Posts: 2,989
    that's all I'd do...maybe some tape to cover the edge's so no one get's cut on them..
  • AnswermanAnswerman Member Posts: 21
    By 'main vent', do you mean the air handler or main trunk line of the air ducts?

    I would recommend against RTV. Instead use some UL-181 rated metal tape (not the cheap $5 unrated stuff, and definitely NOT duck tape). For a temporary or reversible installation, the tape is fine, to make a really good permanent seal, use UL-181 rated, fiber-reinforced duct mastic.

    At large hardware stores you can get a roll of aluminum flashing that works well for patching metal ducts.
    Energy & Sustainability Engineer
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